Test plug and cable for a glucose monitor

ABSTRACT

Methods and apparatuses for electrically connecting a medical glucose monitor to a glucose sensor set, as well as for testing the operation of the glucose monitor, monitor cable and glucose sensor set are provided. In one embodiment, an electric cable comprises a cable member, a first connector and a second connector. The cable member in turn comprises at least one insulated conductor, a conductive shielding layer disposed around the at least one insulated conductor; and an insulating layer disposed around the conductive shielding layer. A glucose monitoring system test plug provides for a releasable electrical connection with the electric cable. In one embodiment, the test plug comprises a housing and a fitting affixed thereto which is adapted to electrically couple the test plug with the electric cable. The test plug further includes an electrical circuit that produces a signal that is read by the glucose monitor to test the operational performance of the glucose monitor and the electric cable when the test plug is coupled to the electric cable and when the electric cable is coupled to the glucose monitor.

RELATED APPLICATIONS

This application claims priority on U.S. Provisional Patent ApplicationNo. 60/121,656, filed Feb. 25, 1999 and which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and devices used for electricallyconnecting medical glucose monitors to glucose sensor electrodes as wellas for testing the operation of the glucose monitors, monitor cables andglucose sensors.

2. Description of the Related Art

Over the years, a variety of implantable electrochemical sensors havebeen developed for detecting or quantifying specific agents orcompositions in a patient's blood. For instance, glucose sensors arebeing developed for use in obtaining an indication of blood glucoselevels in a diabetic patient. Such readings are useful in monitoring oradjusting a treatment regimen which typically includes the regularadministration of insulin to the patient. Thus, blood glucose readingscan improve medical therapies with semi-automated medication infusionpumps of the external type, as generally described in U.S. Pat. Nos.4,562,751; 4,678,408; and 4,685,903; or automated implantable medicationinfusion pumps, as generally described in U.S. Pat. No. 4,573,994, whichare incorporated herein by reference.

Generally, small and flexible electrochemical sensors can be used toobtain periodic readings over an extended period of time. In one form,flexible subcutaneous sensors are constructed in accordance with thinfilm mask techniques in which an elongated sensor includes thin filmconductive elements encased between flexible insulative layers ofpolyimide sheets or similar material. Such thin film sensors typicallyinclude a plurality of exposed electrodes at one end for subcutaneousplacement with a user's interstitial fluid, blood, or the like, and acorresponding exposed plurality of conductive contacts at another endfor convenient external electrical connection with a suitable monitoringdevice through a wire or cable. Typical thin film sensors are describedin commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and5,586,553 which are incorporated herein by reference.

Thin film sensors generate very small electrical signals which can beread by external glucose monitors. These monitors can be portable, andcan be attached to the patient, such as for example, on a belt clip.Applicant's clinical studies have shown that an electrical cable may beprovided for the transmission of these small signals from the sensors tothe glucose monitor. But given the environment in which these cables areused, special characteristics can be useful.

Thus a glucose monitoring system includes connectors between the cables,leads, electrodes and monitors such as those described in pending U.S.patent application Ser. No. 09/346,835, filed Jul. 2, 1999 and entitled“Insertion Set for a Transcutaneous Sensor” and U.S. patent applicationSer. No. 09/377,472, filed Aug. 19, 1999 and entitled “TelemeteredCharacteristic Monitor System and Method of Using Same, both of whichare incorporated herein by reference. Although a well designed systemwill have minimal operational problems, it is possible that a problemmight arise with the integrity of the cables, sensor electrodes ormonitor during their use. The system connectors or the cables may becomeloose or bent, resulting in a poor or open circuit. The sensorelectrodes could degrade. The glucose monitor could become inoperativedue to any number of causes. Thus, it is desirable to provide a systemthat is simple to use so that a patient can easily identify anyoperational problems with the system.

SUMMARY OF THE PREFERRED EMBODIMENTS

A glucose monitoring system test plug as well as an electric cable forelectrically connecting a glucose monitor to a glucose sensor set areprovided. In one embodiment, the electric cable comprises a cablemember, a first connector and a second connector. The cable member inturn comprises at least one insulated conductor, a conductive shieldinglayer disposed around the at least one insulated conductor; and aninsulating layer disposed around the conductive shielding layer.

In one aspect, the first connector comprises a housing having a firstbore which is adapted to receive a sensor set cable fitting and a firstconductive contact disposed within the first bore. The first conductivecontact is electrically coupled to the insulated conductor and isadapted to be removably electrically coupled to a sensor set conductivecontact. In one embodiment of the present invention, a key fitting isformed within the first bore and is adapted to mate with the glucosesensor set in one orientation. There is further provided a releasablecoupler disposed on the housing which is adapted to releasably couplethe housing with the glucose sensor set.

In another aspect, the second connector comprises a housing having asecond bore. The second connector is adapted to releasably couple thesecond connector with the glucose monitor. There is a second conductivecontact disposed within the second bore which is electrically coupled tothe insulated conductor. The second conductive contact also is adaptedto be removably electrically coupled to a glucose monitor conductivecontact.

In yet another aspect, the glucose monitoring system test plug is foruse with a glucose monitor cable which is adapted to electrically coupleto a glucose monitor. The test plug comprises a housing and a fittingaffixed to the housing. The fitting is adapted to electrically couplethe test plug to the glucose monitor cable. The test plug furthercomprises an electrical circuit which is adapted to provide a known testsignal to the cable and the glucose monitor in order to test theoperational performance of the glucose monitor and the glucose monitorcable when the test plug is coupled to the glucose monitor cable andwhen the glucose monitor cable is coupled to the glucose monitor.

In an alternative embodiment, the test plug is provided for use with aglucose monitor. The test plug comprises a housing and a fitting affixedto the housing. The fitting is adapted to electrically couple the testplug to the glucose monitor. The test plug further comprises anelectrical circuit which is adapted to provide a test signal to theglucose monitor to test the operational performance of the glucosemonitor when the test plug is coupled to the glucose monitor.

In yet another embodiment, the test plug can alternatively provide areleasable electrical connection with either the electrical cable or theglucose monitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrical cable for a glucosemonitor in accordance with one embodiment of the inventions.

FIG. 2 is a perspective view of a glucose monitoring system using thecable of FIG. 1.

FIG. 3 is an end plan view of a glucose monitor connector portion of theglucose monitor cable of FIG. 1.

FIG. 4 is a perspective view illustrating the assembly of the glucosemonitor cable of FIG. 1 with an insertion set.

FIG. 5 is a front-end perspective view of a sensor set connector portionof the glucose monitor cable of FIG. 1.

FIG. 6 is a cross-sectional view of a cable member portion of theglucose monitor cable of FIG. 1 as viewed along the lines 6-6 of FIG. 1.

FIG. 7 is a top perspective view of a glucose monitoring system testplug in accordance with another embodiment of the present inventions.

FIG. 8 is a bottom perspective view of the glucose monitoring systemtest plug of FIG. 7.

FIG. 9 is a bottom plan view of the glucose monitoring system test plugof FIG. 7.

FIG. 10 is a schematic diagram of an electrical circuit used in theglucose monitoring system test plug of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments of the present invention. It is understood that otherembodiments may be utilized and structural and operational changes maybe made without departing from the scope of the present invention.

Referring to FIG. 1 there is disclosed a shielded cable 10 constructedin accordance with aspects of the present invention. The cable 10includes a flexible cable member 13 with a monitor connector 11 at oneend and a sensor connector 12 at the opposite end. FIG. 2 illustratesthe use of the cable 10 in an exemplary glucose monitoring system. Thesystem includes a subcutaneous glucose sensor set 20 which is coupled toa glucose monitor 21 by the cable 10. The subcutaneous glucose sensorset 20 uses an electrode-type sensor, as described in more detail below.However, in other applications, the glucose sensor may use other typesof sensors, such as chemical based, optical based or the like. Thesensor shown in FIG. 2 is a surface mounted sensor that usesinterstitial fluid harvested from the skin. Other sensors may be of atype that is used on the external surface of the skin or placed belowthe skin layer of the user.

The glucose monitor 21 of the illustrated embodiment generally includesthe capability to record and store data as it is received from thesensor set 20, and includes either a data port or a wireless transmitterfor downloading the data to a data processor, computer, communicationstation, or the like for later analysis and review. The data processoror computer uses the recorded data from the glucose monitor to determinethe blood glucose history. Thus, one purpose of the glucose monitorsystem is to provide for improved data recording and testing for variouspatient conditions using continuous or near continuous data recording.

The sensor set 20 of the illustrated embodiment is provided forsubcutaneous placement of a flexible sensor, or the like, at a selectedsite in the body of the user. The sensor set 20 includes a hollow,slotted insertion needle 22 and a cannula (not shown) inside the needle22. The needle 22 is used to facilitate quick and easy subcutaneousplacement of the cannula at the insertion site. The cannula includes oneor more sensor electrodes (not shown) which are exposed to the user'sbodily fluids. After insertion, the insertion needle 22 is typicallywithdrawn to leave the cannula with the sensor electrodes in place atthe selected insertion site.

The sensor set 20 includes a mounting base 23 adapted for placement ontothe skin of a user. As shown, the mounting base 23 of the illustratedembodiment is a generally rectangular pad having an underside surfacecoated with a suitable pressure sensitive adhesive layer, with apeel-off paper strip 24 provided to cover and protect the adhesivelayer, until the sensor set 20 is ready for use. Further description ofsuitable needles and sensor sets are found in U.S. Pat. No. 5,586,553,entitled “Transcutaneous Sensor Insertion Set” and U.S. patentapplication Ser. No. 09/346,835, filed Jul. 2, 1999, entitled “InsertionSet for a Transcutaneous Sensor,” which are incorporated herein byreference.

As shown in FIGS. 2 and 3, the glucose monitor 21 is coupled to thesensor set 20 by the cable 10 which electrically couples the monitorconnector 11 to the connector block 25 of the sensor set 20. The monitorconnector 11 of the cable 10 is connected to the glucose monitor 21through a plug receptacle 26 of the monitor 21. The monitor connector 11includes a plurality of pins 31 arranged in a pin snap-in configurationto connect to the receptacle 26 of the glucose monitor 21. In thisembodiment, there are four (4) pins 31, three (3) of which are used forconnection to 3 insulated conductors within the cable 10 and one ofwhich is for a drain (or ground) conductor within the cable 10.

The glucose monitor 21 includes a housing 27 that supports at least oneprinted circuit board, batteries, memory storage, a display screen 28,the plug receptacle 26, and the cable 10 and the monitor connector 11when connected to the plug receptacle 26 of the monitor 21. The lowerportion of the glucose monitor 21 may have an underside surface thatincludes a belt clip, or the like, to attach to a user's clothing.Alternatively, the underside surface may be coated with a suitablepressure sensitive adhesive layer, with a peel-off paper strip normallyprovided to cover and protect the adhesive layer until the glucosemonitor 21 is ready for use. Alternatively, the glucose monitor 21 maybe secured to the body by other methods, such as an adhesiveoverdressing, straps, belts, clips, or the like. Further description ofsuitable glucose monitors are found in U.S. patent application Ser. No.09/377,472, entitled “Telemetered Characteristic Monitor System andMethod of Using the Same” which is incorporated herein by reference.

In other embodiments, the cable 10 may also have a flexible strainrelief portion, as indicated at reference numeral 14 of FIG. 1, tominimize strain on the sensor set 20 and minimize movement of the sensorset 20 relative to the body, which can lead to discomfort or dislodgingof the sensor set 20. The flexible strain relief portion is intended toalso minimize sensor artifacts generated by user movements that causesthe sensor set 20 to move laterally relative to the glucose monitor 21by reducing lateral movement of the sensor connector 12.

The glucose monitor 21 provides power or other signals, through the plugreceptacle 26 to the monitor connector 11 of the cable 10 and thenthrough the cable 10 to the sensor connector 12 of the sensor set 20.These signals are used to drive the sensor electrodes and to speed theinitialization of the sensor set 20, when first placed on the skin.

FIGS. 4 and 5 illustrate a connection arrangement between the sensorconnector 12 portion of the cable 10 of the illustrated embodiment andthe sensor set 20. As shown, the sensor connector 12 has a low profilehousing 40 for comfortable fitting against the body. The housing 40 iscompact in size and can be constructed from lightweight molded plastic.The housing 40 defines a socket fitting 51 for mating slide-fitengagement with a rear cable fitting 41 of a sensor set mounting base23. The socket fitting 51 of the illustrated embodiment has a bore orcylindrical entry portion 52 which leads to a generally D-shaped orhalf-circle step portion 53 positioned within the entry portion 52. Thesocket fitting 51 therefore forms a “keyhole” type fitting which issized to receive the D-shaped “key” portion of the sensor set fitting41.

The socket fitting 51 includes a plurality of conductive contacts 54(FIG. 5) positioned on the step portion 53 for electrically coupledengagement with correspondingly positioned contact pads of the cablefitting 41, when the sensor set 20 and the sensor connector 12 arecoupled together. The conductive contacts 54 of the illustratedembodiment have a leaf spring design to facilitate good electrical andmechanical contact to the sensor set fitting contact pads. Whenassembled, seal rings 42 of the sensor set fitting 41 sealingly engagethe entry portion 52 of the socket fitting 51 to provide a waterresistant connection between the components. Furthermore, the D-shapedgeometry of the interfitting components 41 and 53 facilitate properconductive coupling of the cable 10 to the sensor set 20 in the desiredorientation.

The sensor set 20 and the sensor connector 12 are held together byreleasable couplers, which in the embodiment of FIGS. 4 and 5, includeinterengaging snap fit latch arms 44 of the sensor set 20 and latchrecesses 55 of the connector 12 of the cable 10. As shown, the insertionset mounting base 23 is formed to include the pair of rearwardlyprojecting cantilevered latch arms 44 which terminate at the rearwardends thereof in respective undercut latch tips 43. The latch arms 44 aresufficiently and naturally resilient to provide a living hinge formovement relative to the remainder of the mounting base 23 to permit thelatch arms 44 to be squeezed inwardly toward each other.

The permissible range of motion accommodates snap fit engagement of thelatch tips 43 into a corresponding pair of latch recesses 55 formed inthe housing 40 of the sensor connector 12 on opposite sides of thesocket fitting 51, wherein the latch recesses 55 are lined withindentations which act as latch keepers 56 for engaging the latch tips43. The components can be disengaged for uncoupling when desired bymanually squeezing the latch arms 44 inwardly toward each other forrelease from the latch keepers 56, while axially separating the mountingbase 23 from the sensor connector 12.

For use as a connector between a sensor set and a glucose monitor, thecable 10 includes one or more insulated conductors, and in order toincrease user comfort, should be relatively long and have goodflexibility. However, the electrical signals from the sensor set 20electrodes can be very small (i.e., in the range of 1 to 200 nano amps)thus making the cable susceptible to external electrical noise. Toreduce this susceptibility the cable is preferably shielded andrelatively short. These characteristics would tend in general to make acable less comfortable for a user.

A further source of electrical noise in cables is the triboelectriceffect which is caused by the use of certain electrical insulators.Certain types of insulators, such as for example, Teflon, can be soeffective that when the cable is bent, the electrical charge on thecable will separate but will not reform quickly. When the chargebelatedly reforms, this can appear as a voltage spike or noise on thecable. Thus, while an effective insulator is useful for glucose monitorcables, the insulator preferably should not permit unacceptable levelsof triboelectric noise. Certain insulation materials may provide a goodsolution to the triboelectric effect. However, many of them would notresult in as flexible a cable as is desired.

FIG. 6 shows a cross sectional view of an exemplary embodiment of theflexible cable member 13 of the glucose monitor cable 10. This designstrikes a satisfactory balance between cable flexibility, highinsulation, and low noise characteristics. The cable member 13 includesthree (3) center conductors 61 as well as a drain line 62. The centerconductors 61 are electrically coupled to the conductive contacts 54(FIG. 5) of the sensor connector 12 at one end and are coupled to 3 ofthe 4 pins 31 of the monitor connector 11 at the opposite end. (FIG. 3)The drain line 62 is electrically coupled to the remaining one of thepins 31 of the monitor connector 11 which is electrically grounded. Inthis embodiment, the center conductors 61 each are constructed of 30 AWG40×46 BC bunched stranded copper with a nominal OD of 0.013 inches. Itis believed that alternative constructions for the conductors 61 mayachieve acceptable flexibility if gauges of a number greater than 30 andstrand counts greater than 40 are employed. The drain line 62 isconstructed of 30 AWG 7×0.004 TC concentric stranded copper with anominal OD of 0.012 inches. Other gauges, strand counts and OD's for theconductors 61 and the drain line 62 may be used, however depending uponthe application.

The three conductors 61 are each surrounded by a first insulating jacket63, which in the illustrated embodiment is 8 mils nominal PVC insulationwith a nominal OD of 0.026 inches. An alternative insulation material toPVC is believed to be a polyester material, such as Mil-ene™ which isavailable from W.L. Gore & Associates of Newark, Del. The drain line 62of the illustrated embodiment is not surrounded by a first insulatingjacket.

The three conductors 61, their insulating jackets 63 and the drain line62 are collectively surrounded by a shield 64. The shield 64 isconstructed of 44 AWG tinned copper braid with a nominal thickness of0.007 inches. Other thicknesses and gauges may be used however,depending upon the particular application. The shield 64 serves toprevent or minimize external electromagnetic interference fields fromaffecting the low level signals being transmitted on the conductors 61.The drain line 62 is adjacent to and therefore in electrical contactwith the shield 64 throughout the length of the cable member 13. Becausethe drain line 62 is electrically coupled to the one of the pins 31which is grounded, this serves to ground the shield 64. By grounding theshield 64 in this manner, a separate electrical termination of theshield to any sort of alternative grounding on the monitor connector 11of the cable 10 may be eliminated.

The shield 64 is surrounded by a second insulating jacket 65. The secondinsulating jacket 65 of the illustrated embodiment is constructed of PVC(USP class VI) which is a “food grade” PVC and has a nominal thicknessof 0.010 inch. Alternative acceptable materials to PVC are believed toinclude thermoplastic elastomers such as Santoprene™ which is availablefrom Advanced Elastomers (a division of Monsanto) of Akron, Ohio, or areinforced elastomer based material, Sil-Kore™, which is available fromW.L. Gore & Associates of Newark, Del. The OD of the insulating jacket65, and therefore of the cable 10, is approximately 0.090 inches.Although the illustrated embodiment of the outer jacket 65 has a nominalthickness of 0.010 inches and an OD of 0.090, inches, it is believedthat nominal thicknesses of 0.006 inches or greater and OD's of 0.110inches or less may be employed and achieve acceptable results.

When constructed in accordance with the previously-described embodiment,it is believed that the cable 10 will have triboelectric noisecharacteristics of no more than approximately 50 to 150 micro volts perAAMI ECG 5/83 test. This construction results in a cable member 13 whichstrikes a satisfactory balance between maximum insulation and minimaltriboelectric noise. Moreover, the cable 10 is small in diameter andrelatively long and flexible, thus providing a greater degree of usercomfort. However, these embodiments may also be used for shorter cablesused to connect various components in telemetered systems, such as thatdescribed in U.S. patent application Ser. No. 09/377,472 and entitled“Telemetered Characteristic Monitor System and Method of Using Same.”

Referring now to FIG. 7, a test plug 70 is disclosed that can simulatethe glucose sensor electrodes, or the combination of the glucose sensorelectrodes and the cable 10 of a glucose monitoring system. If anoperating problem occurs while the glucose monitoring system is beingused, the test plug 70 provides diagnostic information that can helpindicate if a glucose sensor, the cable or the glucose monitor isoperating normally.

The test plug 70 includes two connectors. Each connector facilitates thetesting of a different component of a glucose monitoring system. Amonitor connector 72 allows the device to plug into the glucose monitor21 in place of the cable 10 so the monitor can be checked independentlyfrom the rest of the system. A cable fitting 73 allows the device toplug into the cable 10 in place of the sensor set 20 so that theoperation of the cable 10 can also be verified.

As will be described in more detail below, the test plug 70 is a sensorsimulator that, in one embodiment, can return a constant current of thesame magnitude as is produced by the sensor electrodes during normalin-vivo operation. This current is measured by the monitor 21 and isreported on the display screen 28 of the monitor 21. (FIG. 2) From thedisplay screen 28, the user can view the test current and verify thatthe monitor is reporting the correct signal current with the expectedaccuracy. This can be accomplished when the test plug 70 is pluggeddirectly into the monitor or when it is plugged into the distal end ofthe cable 10.

The ability to perform such simple performance checks in the field isexpected to offer users the opportunity to troubleshoot system problemswith greater ease and confidence.

Referring to FIG. 10, the test plug simulates the presence of an actualsensor electrode to produce a signal current that the monitor canmeasure. Monitor connector pins 79-82 are disposed in the monitorconnector 72 portion of the test plug 70 (FIG. 7) and are adapted fordirect connection to the plug receptacle 26 of the glucose monitor 21.(FIG. 2) In one embodiment, the simulator has an electrical circuit 1003that includes a first resistor 1001 connected between the monitorconnector pin 80 which simulates a reference electrode connection andthe monitor connector pin 79 which simulates a working electrodeconnection. The test current produced depends upon the voltage providedby the monitor 21 and the value of the resistor between the simulatedreference and working electrode connections. In one embodiment, a testcurrent of 27 nA is developed with a nominal monitor voltage of 535 mVwhere the first resistor 1001 is 20 million ohms.

A second resistor 1002 is placed between the monitor connector pin 81which simulates a counter electrode connection and the monitor connectorpin 80. The second resistor 1002 is chosen to be of equal value, or 20million ohms, so that the voltage at the simulated counter electrode 81will be twice that of the monitor voltage as measured between simulatedelectrodes 79 and 80. Choosing the second resistor value to produce avoltage twice that of the monitor voltage facilitates verifying themonitor voltage value. Monitor connector pin 82 simulates a connectionto the cable drain line 62 (FIG. 6) and therefore is electricallyisolated from the resistors 1001 and 1002.

Still referring to FIG. 10, a plurality of contact pads 75 are disposedin the cable fitting 73 portion of the test plug 70 (FIG. 7) and areadapted for electrical connection to the sensor connector 12 of thecable 10. (FIG. 5) When connected to the cable 10, the test plug 70continues to simulate the presence of an actual sensor electrode.However, it produces a signal current that travels through the cable 10to the monitor for measurement.

The contact pads 75 are connected to the resistors 1001 and 1002 in thesame fashion as the monitor connector pins 79-81. Therefore, the mannerin which the test current is generated through the contact pads 75 andthrough the cable 10 is the same as was previously described.

It will be appreciated that although the electrical circuitry shown inFIG. 10 has resistors arranged to produce a test current, many othercircuitry arrangements comprised of other, known, electrical components,such as capacitors, inductors, semiconductor devices and voltagesources, can be incorporated in the test plug 70 to provide a suitabletest current or other test signal.

Referring now to FIGS. 7-9, one embodiment of the test plug 70 of thepresent invention is shown. The test plug 70 includes a housing 71 whichencloses the electrical circuitry, such as that shown in FIG. 10. At oneend of the test plug 70 is the monitor connector fitting 72. At theopposite end is the cable fitting 73.

The cable fitting 73 is sized for mating slide-fit engagement with thesocket fitting 51 of the cable 10. (FIG. 5) The cable fitting 73connects to the cable 10 in the same manner as the glucose sensor set20. Accordingly, the cable fitting 73 is the same as or similar to thesensor fitting 41 and likewise includes a D-shaped fitting key 74 whichis received by the cylindrical entry portion 52 of the socket fitting51. (FIG. 5) The generally D-shaped step portion 53 of the fitting 51receives the D-shaped fitting key 74 of the cable fitting 73 portion ofthe test plug 70. (FIG. 7) As shown, the cable fitting 73 includes theplurality of conductive contact pads 75 positioned on the flat portionof the fitting key 74 (FIG. 8) for electrically coupled engagement withthe conductive contacts 54 (FIG. 5) of the cable 10. The conductive pads75 are further coupled to the resistors 1001 and 1002 shown in FIG. 10.

The cable fitting 73 includes positioning rings 76 situated around thetubular portion of the cable fitting 73. Because the insertion set 20includes seal rings 42 for a seal tight engagement with the socketfitting 51 of the cable 10 (FIG. 4), the positioning rings 76 on thetest plug 70 serve as a counterpart to the seal rings 42 and are used toproperly center the cable fitting 73 in the socket fitting 51. TheD-shaped geometry of the interfitting components 74 and 53 insure properorientation for correct conductive coupling of the cable 10 to the testplug 70. Although a D-shaped geometry is shown in FIG. 4, othergeometries, such as triangles, notches and the like, can be employed toprovide proper orientation.

Referring again to FIGS. 5 and 7, the test plug 70 and the sensorconnector 12 portion of the cable 10 are retained in releasable coupledrelation by interengaging snap fit latch members. As shown, the testplug housing 71 is formed to include a pair of rearwardly projectingcantilevered latch arms 77 which terminate at the rearward ends thereofin respective undercut latch tips 78. The latch arms 77 are sufficientlyand naturally resilient for movement relative to the remainder of thehousing 71 to permit the latch arms 77 to be squeezed inwardly towardeach other.

The permissible range of motion accommodates snap fit engagement of thelatch tips 78 into a corresponding pair of latch recesses 55 formed inthe sensor connector housing 40 on opposite sides of the socket fitting51, wherein the latch recesses 55 are lined with latch keepers 56 forengaging the latch tips 78. With this arrangement, the user is able tohear a clicking noise and feel the test plug snap into place. Thecomponents can be disengaged for uncoupling when desired by manuallysqueezing the latch arms 77 inwardly toward each other for release fromthe latch keepers 56, while axially separating the test plug 70 from thesensor connector 12 portion of the cable 10.

The monitor connector 72 portion of the test plug 70 can be electricallycoupled directly to the glucose monitor 21 through the plug receptacle26 of the monitor 21. (FIG. 2) The monitor connector 72 connects to theglucose monitor 21 in the same manner as the cable 10. The monitorconnector 72 has a plurality of pins 79-82 for a snap-in configurationto the glucose monitor 21. (FIG. 9) In this embodiment, the pins 79-81are used for connection to the test plug resistors 1001 and 1002 asshown in FIG. 10.

Having described the structure of the test plug 70, it can be seen howthe test plug 70 can be used to provide diagnostic information that canhelp indicate if a glucose sensor, the cable or the glucose monitor isoperating normally. Referring generally to FIGS. 2 and 7, if the display28 of the monitor 21 indicates that there is a malfunction, the sensorset 20 can be disconnected from the cable 10. The sensor connector 12portion of the cable can then be connected to the cable fitting 73portion of the test plug 70. By pressing the appropriate buttons on themonitor 21, the monitor 21 can apply a test voltage through the cable 10and the resistors 1001 and 1002 of the test plug 70 and measure theresulting current. The value of the current can be displayed on themonitor screen 28. If the value of the current falls within anacceptable range, then it is known that the monitor 21 and the cable 10are operating properly. The operational problem therefore likely lies inthe sensor set 20 which can be replaced by the user.

On the other hand, if the measured current is outside of the acceptablerange of values, then the problem may lie in either the cable 10 or themonitor 21 or both. The user then disconnects the cable 10 from themonitor 21 and from the test plug 70. The monitor connector 72 portionof the test plug 70 may then be connected directly to the plugreceptacle 26 of the monitor 21. Once again the appropriate buttons onthe monitor 21 are pressed by the user to cause a test voltage to beapplied from the monitor 21 directly to the test plug 70 therebymeasuring the resulting current. If the value of the current asdisplayed on the monitor screen 28 falls within an acceptable range,then it may be deduced that the monitor 21 is likely operating properlyand that the problem likely lies in the cable 10. The cable 10 can bereplaced and the system tested with a new cable to verify properoperation. On the other hand if the value of the current falls outsidethe acceptable range, then the monitor 21 is likely to have a problem.If the user is unable to locate and correct the monitor 21 problem, themonitor can be sent to a repair facility.

Although shown for use with the cable 10 and the monitor 21, furtherembodiments of the test plug may be used in telemetered systems to testthe various components, such as shown and described in U.S. patentapplication Ser. No. 09/377,472 and entitled “Telemetered CharacteristicMonitor System and Method of Using Same.”

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than the foregoing description,and all changes which come within the meaning and range of equivalencyof the claims are therefore intended to be embraced therein.

1. An electric cable having a proximal end and a distal end, theelectric cable for use with a glucose monitor and a glucose sensor andcomprising: a first connector at the proximal end of the cable; a secondconnector at the distal end of the cable; and a cable member affixed tothe first and the second connectors, the cable member comprising: atleast one insulated conductor having a gauge number greater than 29 anda strand count greater than 39; a conductive shielding layer disposedaround the at least one insulated conductor; and an insulating layerdisposed around the conductive shielding layer, the insulating layerbeing made of a material selected from the group consisting of USP classVI PVC and thermoplastic elastomer and reinforced elastomer, and whereinthe insulating layer has an OD of less than 0.110 inches.
 2. Theelectric cable of claim 1 wherein the insulating layer has nominalthickness of greater than 0.005 inches.
 3. The electric cable of claim 1wherein the at least one insulated conductor has an insulation layermade of a material selected from the group consisting of PVC andpolyester.
 4. The electric cable of claim 1, further comprising a drainline conductor disposed within the conductive shielding layer, the drainline conductor being adjacent to and in electrical connection with theconductive shielding layer.
 5. A method of electrically connecting aglucose monitor to a glucose sensor, the method comprising: connectingthe glucose monitor to the proximal end of an electric cable comprising:at least one insulated conductor having a gauge number greater than 29and a strand count greater than 39; a conductive shielding layerdisposed around the at least one insulated conductor; and an insulatinglayer disposed around the conductive shielding layer, the insulatinglayer being made of a material selected from the group consisting of USPclass VI PVC and thermoplastic elastomer and reinforced elastomer, andwherein the insulating layer has an OD of less than 0.110 inches; andconnecting the glucose sensor to the distal end of the electric cable.6. The method of claim 5 wherein the insulating layer has nominalthickness of greater than 0.005 inches.
 7. The method of claim 5 whereinthe at least one insulated conductor has an insulation layer made of amaterial selected from the group consisting of PVC and polyester.
 8. Themethod of claim 5 wherein the electric cable further comprises a drainline conductor disposed within the conductive shielding layer, the drainline conductor being adjacent to and in electrical connection with theconductive shielding layer.
 9. A method of electrically connecting aglucose monitor to a glucose sensor set, the method comprising:connecting a first connector of an electric cable to the glucose sensorset, the electric cable further having a cable member, and a secondconnector, the glucose sensor set having a sensor set cable fitting anda sensor set conductive contact, the cable member comprising: at leastone insulated conductor; a conductive shielding layer disposed aroundthe at least one insulated conductor; and an insulating layer disposedaround the conductive shielding layer; the first connector comprising: afirst connector housing having a first bore, the first bore adapted toreceive the sensor set cable fitting; and a first conductive contactdisposed within the first bore, the first conductive contact beingelectrically coupled to the at least one insulated conductor, the firstconductive contact further being removably electrically coupled to thesensor set conductive contact; and connecting the second connector tothe glucose monitor having a glucose monitor conductive contact, thesecond connector comprising: a second connector housing having a secondbore, the second connector housing adapted to releasably couple thesecond connector with the glucose monitor; and a second conductivecontact disposed within the second bore, the second conductive contactbeing electrically coupled to the at least one insulated conductor, thesecond conductive contact further being removably electrically coupledto the glucose monitor conductive contact.
 10. The method of claim 9wherein the at least one insulated conductor has a gauge number greaterthan 29 and has a strand count greater than 39, wherein the insulatinglayer is made of a material selected from the group consisting of USPclass VI PVC and thermoplastic elastomer and reinforced elastomer, andwherein the electric cable has an OD of less than 0.110 inches.
 11. Themethod of claim 9 wherein the first connector further comprises a keyfitting formed within the first bore, the key fitting being adapted tomate with the glucose sensor set in one orientation.
 12. The method ofclaim 9 wherein the first connector further comprises a releasablecoupler disposed on the first connector housing, the releasable coupleradapted to releasably couple the first connector housing with theglucose sensor set.
 13. The method of claim 9 wherein the glucosemonitor has a ground contact, and wherein the cable member furthercomprises a drain conductor disposed within the conductive shieldinglayer, and wherein the second connector further comprises a drain lineconductive contact disposed within the second bore, the drain lineconductive contact being electrically coupled to the drain conductor,the drain line conductive contact further being adapted to be removablyelectrically coupled to the glucose monitor ground contact.
 14. Anelectric cable for electrically connecting a glucose monitor to aglucose sensor set, the electric cable comprising: means for providingan electrical path between the glucose monitor and the glucose sensorset; means for insulating the electrical path providing means; means forshielding the electrical path providing means against externalelectromagnetic fields; and means for insulating the shielding means.15. The electric cable of claim 14 further comprising means forgrounding the shielding means.